AT5200 [AGC038C] LCMs

i=1nj=i+1nlcm(Ai,Aj)\sum_{i=1}^n\sum_{j=i+1}^n\text{lcm}(A_i,A_j)

i=1nj=1nlcm(Ai,Aj)i=1nAi2\frac{\sum_{i=1}^n\sum_{j=1}^n\text{lcm}(A_i,A_j)-\sum_{i=1}^nA_i}{2}

阅读全文 »